JERUSALEM -LRB- CNN -RRB- -- Former U.S. Rep. Cynthia McKinney -- who was aboard a ship the Israeli navy intercepted this week -- is in a detention center and will be returned to the United States , the U.S. Embassy said .

Former U.S. Rep. Cynthia McKinney , D-Georgia , refuses to sign Israeli deportation papers , the U.S. Embassy says .

McKinney was among those on a ship that the Israeli Defense Forces said violated an Israeli blockade and crossed into Gazan waters on Tuesday .

The Israeli navy gained control of the ship and took McKinney and about 20 people into custody , said the Free Gaza Movement , a human rights group that sent the ship .

The group said the ship , which it calls Spirit of Humanity , was carrying humanitarian aid to Gaza .

McKinney served six terms in the House of Representatives as a Democrat from Georgia and was the Green Party 's 2008 presidential nominee .

The ex-lawmaker is in the Givon immigration detention center in the central Israeli city of Ramle , the U.S. Embassy said .

She has been given deportation papers but has refused to sign them , the embassy said .

She will be held for three more days , assuming she does not sign the papers , and then will be sent back to the United States , the embassy added .

The location of others taken into custody was not immediately known .

The IDF said the ship , which it called the Arion , had been warned while at sea that it would not be allowed to enter Gazan waters `` because of security risks in the area and the existing naval blockade . ''

The IDF said the cargo boat disregarded all warnings and entered Gazan coastal waters . An Israeli navy force intercepted , boarded and took control of the vessel , directing it toward Ashdod , Israel , the IDF said .

The boat 's crew would `` be handed over to the proper authorities , '' the military said .

Without naming who was on the boat , the IDF confirmed that the incident was the same detailed by the Free Gaza Movement .

According to the Free Gaza group , McKinney said , `` This is an outrageous violation of international law against us . Our boat was not in Israeli waters , and we were on a human rights mission to the Gaza Strip '' before authorities confiscated cell phones .

Also aboard was Mairead Maguire , who co-founded a group that worked for peace in Northern Ireland . Maguire and co-founder Betty Williams received the Nobel Peace Prize in 1976 for their work .

Free Gaza said the voyage is the eighth such trip the group has launched . Five succeeded , the group said , but the Israeli military stopped attempts in January 2008 and December .

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Ex-U.S. Rep. Cynthia McKinney is in Israeli detention center , U.S. Embassy says

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McKinney will be returned to U.S. in three days , embassy says

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Boat with McKinney enters Gazan waters , violates blockade , Israel says

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Human rights group says ship was carrying humanitarian aid to Gaza